(1) Field of the Invention
The present invention pertains to a dual-pressure jack.
(2) Description of the Background
It sometimes happens, for example, in resistance spot welding, that two different pressures have to be successively exerted at one point of a material: one higher pressure to deform the material and the other lower pressure to hold the deformed part against the surface of another material during welding. Currently, for operations of this type, it is possible either to use different jack fluid pressures or to combine a jack with a cam-operated positioning device. In both cases, the apparatus used is a complicated and bulky one.
The object of the present invention is a jack which can be used to successively exert two different pressures at different positions of the outgoing rod of the jack, through only one control fluid pressure, using simple and compact means.